Microelectronic devices, such as memory devices, microprocessors, and light emitting diodes, typically include one or more semiconductor dies mounted to a substrate and encased in a plastic protective covering. Semiconductor dies include functional features, such as memory cells, processor circuits, and interconnecting circuitry. Semiconductor dies also typically include bond pads electrically coupled to the functional features. The bond pads are electrically connected to pins or other types of terminals that extend outside the protective covering for connecting the semiconductor die to busses, circuits, or other assemblies.
Semiconductor die manufacturers are under increasing pressure to reduce the volume occupied by the die and yet increase the capacity and/or speed of the resulting encapsulated assemblies. To meet these demands, semiconductor die manufacturers often stack multiple dies on top of each other to increase the capacity or performance of the device within the limited volume on the circuit board or other element to which the dies are mounted. In many applications, the dies are stacked on each other before being encapsulated to form a three-dimensional package.
The stacked semiconductor dies are typically electrically connected by solder bumps or other electrical connectors that are attached to under-bump metal (UBM) structures. The UBM structures are typically formed by depositing a copper seed structure onto a wafer, forming a mask on the copper seed structure having openings aligned with bond pads on the die, plating copper onto the seed structure, and then plating one or more other materials over the copper to form UBM structures. The top-most material of the UBM structure is typically selected to promote wetting for subsequently forming interconnects on the top-most material. After forming the UBM structures, microbumps of solder material are formed over the top-most material of the UBM structures to serve as interconnects. After forming the UBM structures and microbumps, the mask is removed and the exposed portions of the seed structure are removed using a suitable wet etch to form isolated UBM structures and microbumps. The present technology is directed to improved UBM structures and methods of manufacturing UBM structures.